1. Field of the Invention
The present invention relates generally to a gas turbine cooled stationary blade and more particularly to a gas turbine cooled stationary blade which is suitably applied to a second stage stationary blade and is improved so as to have an enhanced strength against thermal stresses and an enhanced cooling effect.
2. Description of the Prior Art
FIG. 10 is a cross sectional view showing a gas path portion of front stages of a gas turbine in the prior art. In FIG. 10, a combustor 30 comprises a fitting flange 31, to which an outer shroud 33 and inner shroud 34 of a first stage stationary blade (1c) 32 are fixed. The first stage stationary blade 32 has its upper and lower ends fitted to the outer shroud 33 and inner shroud 34, respectively, so as to be fixed between them. The first stage stationary blade 32 is provided in plural pieces arranged in a turbine circumferential direction and fixed to a turbine casing on a turbine stationary side. A first stage moving blade (1s) 35 is provided on the downstream side of the first stage stationary blade 32 in plural pieces arranged in the turbine circumferential direction. The first stage moving blade 35 is fixed to a platform 36, and this platform 36 is fixed around a turbine rotor disc, so that the moving blade 35 rotates together with a turbine rotor. A second stage stationary blade (2c) 37 is provided, having its upper and lower ends fitted likewise to an outer shroud 38 and inner shroud 39, respectively, on the downstream side of the first stage moving blade 35. The second stage stationary blade is provided in plural pieces arranged in the turbine circumferential direction on the turbine stationary side. Further downstream thereof, a second stage moving blade (2s) 40 is provided, being fixed to the turbine rotor disc via a platform 43. Such a gas turbine as having the mentioned blade arrangement is usually constructed of four stages. A high temperature combustion gas 50 generated by combustion in the combustor 30 flows through the first stage stationary blades (1c) 32 and, while flowing through between the blades of the second to fourth stages, the gas expands to rotate the moving blades 35, 40, etc. to thus give rotational power to the turbine rotor, The gas 50 is then discharged.
FIG. 11 is a perspective view of the second stage stationary blade 37 mentioned with respect to FIG. 10. In FIG. 11, the second stage stationary blade 37 is fixed to the outer shroud 38 and inner shroud 39. The outer shroud 38 is formed in a rectangular shape having the periphery thereof surrounded by end flanges 38a, 38b, 38c, and 38d and a bottom plate 38e in a central portion thereof. Likewise, the inner shroud 39 is formed in a rectangular shape having a lower side (or inner side) peripheral portion thereof surrounded by end flanges 39a and 39c and fitting flanges 41 and 42 and a bottom plate 39e in a central portion thereof. Cooling of the second stage stationary blade 37 is done such that cooling air flows in from the outer shroud 38 side via an impingement plate (not shown) to enter an interior of the shroud 38 for cooling the shroud interior and then to enter an opening of an upper portion of the blade 37 to flow through blade inner passages for cooling the blade 37. The cooling air, having so cooled the blade 37, flows into an interior of the inner shroud 39 for cooling thereof and is then discharged outside.
FIG. 12 is a cross sectional view of the second stage stationary blade. In FIG. 12, numeral 61 designates a blade wall, which is usually formed to have a wall thickness of 4 mm. Within the blade, there is provided a rib 62 to form two sectioned spaces on blade leading edge and trailing edge sides. An insert 63 is inserted into the space on the blade leading edge side and an insert 64 is inserted into the space on the blade trailing edge side. Both of the inserts 63 and 64 are inserted into the spaces with a predetermined gap being maintained from an inner wall surface of the blade wall 61. A plurality of air blow holes 66 are provided in and around each of the inserts 63 and 64 so that cooling air in the blade may flow out therethrough into the gap between the blade wall 61 and the inserts 63 and 64. Also, a plurality of cooling holes 60 for blowing out the cooling air are provided in the blade wall 61 at a plurality of places of a blade leading edge portion and blade concave and convex side portions, so that the cooling air which has flowed into the gap between the blade wall 61 and the inserts 63, 64 may be blown outside of the blade for effecting shower head cooling of the blade leading edge portion and film cooling of the blade concave and convex side portions to thereby minimize the influences of the high temperature therearound.
In the gas turbine stationary blade as described above, the cooling structure is made such that cooling air flows in from the outer shroud side for cooling the interior of the outer shroud and then flows into the interior of the stationary blade for cooling the inner side and outer side of the blade, and further flows into the interior of the inner shroud for cooling the interior of the inner shroud. However, the second stage stationary blade is a blade which is exposed to high temperature, and there are problems caused by the high temperature, such as deformation of the shroud, thinning of the blade due to oxidation, peeling of the coating, the occurrence of cracks at a blade trailing edge fitting portion or a platform end face portion, etc.
In view of the problems in the gas turbine stationary blade, especially the second stage stationary blade, in the prior art, it is an object of the present invention to provide a gas turbine cooled stationary blade which is suitably applied to the second stage stationary blade and is improved in the construction and cooling structure such that a shroud or blade wall, which is exposed to a high temperature to be in a thermally severe state, may be enhanced in strength and cooling effect so that deformation due to thermal influences and the occurrence of cracks may be suppressed.
In order to achieve the object, the present invention provides the following structures (1) to (7).
(1) A gas turbine cooled stationary blade comprises an outer shroud, an inner shroud and an insert of a sleeve shape, having air blow holes, inserted into an interior of the blade between the outer and inner shrouds. The blade is constructed such that cooling air entering the outer shroud flows through the insert to be blown through the air blow holes, to be further blown outside of the blade through cooling holes provided so as to pass through a blade wall of the blade, to be led into the inner shroud for cooling thereof, and to then be discharged to the outside. A blade wall thickness in an area of 75% to 100% of a blade height of a blade leading edge portion of the blade is made thicker toward the insert than a blade wall thickness of other portions of the blade. The blade is provided therein with a plurality of ribs arranged up and down between 0% and 100% of the blade height on a blade inner wall on a blade convex side. The plurality of ribs extend in a blade transverse direction and protrude toward the insert. The outer and inner shrouds are provided therein with cooling passages arranged in shroud both side end portions on blade convex and concave sides of the respective shrouds so that cooling air may flow therethrough from a shroud front portion, or a blade leading edge side portion, of the respective shrouds to a shroud rear portion, or a blade trailing edge side portion, of the respective shrouds to then be discharged outside through openings provided in the shroud rear portion. The inner shroud is further provided therein with a plurality of cooling holes arranged along the cooling passages on the blade convex and concave sides of the inner shroud. The plurality of cooling holes communicate at one end of each hole with the cooling passages and open at the other end in a shroud side end face so that cooling air may be blown outside through the plurality of cooling holes.
(2) A gas turbine cooled stationary blade as mentioned in (1) above can have the inner shroud provided, in an entire portion of the shroud front portion, including the shroud both side end portions thereof, with a space where a plurality of erect pin fins are provided. The space communicates at the shroud both side end portions with the cooling passages on the blade convex and concave sides of the inner shroud.
(3) A gas turbine cooled stationary blade as mentioned in (1) above can have the cooling holes that are provided to pass through the blade wall provided only on the blade convex side.
(4) A gas turbine cooled stationary blade as mentioned in (1) above can have the outer and inner shrouds provided with a flange the side surface of which coincides with a shroud side end face on the blade convex and concave sides of the respective shrouds, so that two mutually adjacent shrouds in a turbine circumferential direction of the respective shrouds may be connected by a bolt and nut connection via the flange.
(5) A gas turbine cooled stationary blade as mentioned in (1) above can have a shroud thickness, near a specific place where thermal stress may easily arise, including the blade leading edge and trailing edge portions, in a blade fitting portion of the outer shroud, made thinner than a shroud thickness of other portions of the outer shroud.
(6) A gas turbine cooled stationary blade as mentioned in (1) above has the blade leading edge portion made in an elliptical cross sectional shape in the blade transverse direction.
(7) A gas turbine cooled stationary blade as mentioned in (1) above can have the gas turbine cooled stationary blade a gas turbine second stage stationary blade.
In the invention (1), the blade wall thickness in the area of 75% to 100% of the blade height of the blade leading edge portion is made thicker. Thereby, the blade leading edge portion near the blade fitting portion to the outer shroud (at 100% of the blade height), where there are severe influences of bending loads due to the high temperature and high pressure combustion gas, is reinforced and rupture of the blade is prevented. Also, the plurality of ribs are provided up and down between 0% and 100% of the blade height, extending in the blade transverse direction and protruding from the blade inner wall on the blade convex side, whereby the blade wall in this portion is reinforced and swelling of the blade is prevented. Further, the outer shroud and the inner shroud, respectively, are provided with the cooling passages in the shroud both side end portions so that cooling air entering the shroud front portion flows through the cooling passages to then be discharged outside of the shroud rear portion. Thereby, both of the side end portions on the blade convex and concave sides of the shroud are cooled effectively. Also, the inner shroud is provided with the plurality of cooling holes in the shroud both side end portions so that cooling air flowing through the insert and entering the shroud front portion is blown outside through the plurality of cooling holes. Thus, both of the side end portions on the blade convex and concave sides of the inner shroud are effectively cooled.
In the invention (1), there are provided the structure of the blade fitting portion to the outer shroud, the fitting of the plurality of ribs in the blade, the structure of the cooling passages, and the plurality of cooling holes in the outer and inner shrouds. The cooling effect of the blade fitting portion and the outer and inner shrouds is thereby enhanced and occurrence of cracks due to thermal stresses can be prevented.
In the invention (2), the space where the plurality of erect pin fins are provided is formed in the entire shroud front portion, including both side end portions of the shroud. The cooling area having the pin fins is thereby enlarged, as compared with the conventional case where there has been no such space having the pin fins in both side end portions of the shroud front portion. Thus, the cooling effect by the pin fins is enhanced and the cooling of the shroud front portion by the invention (1) is further ensured.
In the invention (3), the cooling holes of the blade are not provided on the blade concave side, but on the blade convex side only, where there are influences of the high temperature gas, whereby the cooling air can be reduced in the volume.
In the invention (4), the flange is fitted to the outer and inner shrouds. Two mutually adjacent shrouds in the turbine circumferential direction of the outer and inner shrouds, respectively, can be connected by the bolt and nut connection via the flange. The strength of fitting of the shrouds is thereby well ensured and the effect of suppressing the influences of thermal stresses by the invention (1) can be further enhanced.
In the invention (5), in the blade fitting portion where the blade is fitted to the outer shroud, the shroud thickness near the place where the thermal stress may arise easily, for example, the blade leading edge and trailing edge portions, is made thinner so that the thermal capacity of the shroud of this portion may be made smaller. The temperature difference between the blade and the shroud is thereby made smaller and the occurrence of thermal stresses can be lessened.
In the invention (6), the blade leading edge portion has an elliptical cross sectional shape in the blade transverse direction. The gas flow coming from the front stage moving blade, having a wide range of flowing angles, may be securely received, whereby the aerodynamic characteristic of the invention (1) is enhanced, imbalances in the influences of the high temperature gas are eliminated and the effects of the invention (1) can be further enhanced.
In the invention (7), the gas turbine cooled stationary blade of the present invention is used as a gas turbine second stage stationary blade and the enhanced strength against thermal stresses and the enhanced cooling effect can be efficiently obtained.